The present invention relates to balloon cannulas, and in particular to retrograde cannulas used in the delivery of cardioplegia.
Retrograde cannulas are commonly employed during certain cardiac surgical procedures, in order to deliver cardioplegia into coronary veins to effect cardiac arrest by depolarizing cell membranes (see U.S. Pat. No. 5,395,331).
A conventional retrograde cannula 100 is depicted in FIG. 5. In order to occlude the coronary sinus, the distal end 102 of the cannula 100 includes an inflatable balloon 104 which, when inflated, seals against a wall of the coronary sinus. Balloons may be of the manual-inflating or auto-inflating type. In the manual inflating type, fluid is supplied to or removed from the balloon by means of a syringe. In the auto-inflating type (also referred to as self-inflating), the balloon is in fluid communication with an infusion lumen through which is the CPG delivered to the blood stream, and is inflated by the CPG.
The cannula itself is highly flaccid and would be difficult to install in its normal flaccid state. Accordingly, it is conventional to insert a stylet 106 into the cannula to stiffen it. The stylet is inserted into the proximal end of an infusion lumen that is to be used to deliver the CPG to the patient via outlet 108. After the cannula has been installed, the stylet is removed so that CPG can be delivered through the infusion lumen. However, upon removal of the stylet, it is possible for there to occur a backflow of blood through the infusion lumen from its distal end to its proximal end, until the proximal end is closed off, e.g., by a clamp. The backflowing blood could potentially come into contact with surgical personnel, which is undesirable from a health safety standpoint.
Therefore, it would be desirable to provide a retrograde cannula which avoids a back-flow of blood when removing the stylet. Moreover, after the cannula has been inserted, it may become dislodged from its intended position, especially in the case of an auto-inflate cannula wherein the balloon becomes deflated when the delivery of CPG is halted, so that the distal end of the cannula is no longer supported. In order to reposition the cannula, it may be necessary to re-insert the stylet, which requires removal of a CPG-supply conduit attached to the infusion lumen.
Therefore, it would also be desirable to provide a retrograde cannula which avoids the need to disconnect a fluid supply conduit when re-inserting the stylet.